The present invention relates to an image receiving sheet, which is further transferable and an imaging method by the use thereof, and in particular to a transferable image receiving sheet suitable for thermally melted transfer for use in laser recording and an imaging method by the use thereof. Specifically, the invention relates to an image receiving sheet, which further transfers the received image and which exhibits superiority in sensitivity, in solid area density quality, in fine-line reproduction and in storage stability as a print proof employing printing paper or film substrate as a final recording medium and in addition has image glossiness approximating the surface of the final recording medium.
Along with the spread of imaging technologies from digital data, specifically in the field of graphic arts, there is increased the need for digital color proofs (hereinafter, also denoted as DDCP). In such DDCP, color reproduction and reproducible stability of printed matter are required, and a laser thermal transfer technology is applied thereto. Exemplarily, there is disclosed a technique, in which using an ink sheet for use in laser thermal transfer which comprises a light-to-heat conversion layer and a coloring material layer, and an image receiving sheet for use in laser thermal transfer which comprises an image receiving layer accepting an ink layer of the ink sheet and a thermally softening layer (heat-softening layer), the ink layer side of the ink sheet is allowed to face the image receiving layer side of the image receiving sheet, imagewise laser exposure is conducted from the ink sheet side, and the ink layer is thermally transferred onto the image receiving layer side through light-to-heat conversion, followed by thermal transfer from the image receiving sheet carrying the image onto the final recording medium.
Such a type of DDCP, in which a final image can be outputted on the same kind of paper as used in printing is preferable as a final proof sample in terms of half tone dot output and use of printing colorant and printing paper. Various kinds of paper are used in printing, and art paper, coated paper, matte paper, slightly coated paper and non-coated paper are cited according to the kind thereof.
Recently, desire has increased to use a broader range of paper for the foregoing DDCP. In response to such desire, a technique for improving the physical property of the heat-softening layer, thereby improving transferability onto paper, ranging from matte paper to fine-quality paper, has been disclosed in JP-A 2001-138648. It is a point that the user-desired level of proofs corresponding to the printing paper is not only being transferred onto paper but also the paper being similar to printing matter with respect to non-imaging/imaging areas.
Techniques regarding the following items 1) through 3) were disclosed as a prior art for glossiness adjustment by the inventors of this application:
1) A so-called ink-on recording system in which after forming an ink image on an intermediate medium, the ink image is further transferred to the final recording medium;
2) A method in which thermal deformability of the intermediate transfer medium is raised, thereby enhancing ability of following paper at the time of retransfer and closely resembling non-imaging areas of the paper; and
3) a method and material, in which in a system of transferring the whole image receiving layer having an ink image is transferred, the image receiving layer surface is roughened to approximating the non-imaging area of the final recording medium.
However, in ink-on recording system of 1), problems arose that imaging areas were roughened at the time of retransfer and peeling, lowering glossiness in the imaging areas, and quality was unsuitable when high glossy paper such as art paper was used. With regard to the method of 2), there were two problems to be solved. Thus, the first problem was that when transferred to and peeled from the final recording medium, the peeling face followed unevenness of the paper surface and peeling was so severe that enhancing thermal deformability without providing a peelable interlayer scarcely causing thermal deformation damaged the final recording medium with high probability. The second problem is that in the case of smooth surfaced paper such as art paper, glossiness is not lowered to the level of the paper surface even after applying high heat or pressure and is still unsuitable. Concerning the method 3), the surface-roughened image receiving layer is wholly transferred, producing no roughened imaging area, as is caused in the system 1), and even for smooth art paper, glossiness of non-imaging areas, which is superior to the method 2) can be adjusted to a level equivalent to the intended final recording medium. Accordingly, the method 3) is preferable in terms of adjusting glossiness.
For such an intermediate transfer medium, various performance items other than glossiness are required. For example, the writing speed is an important factor and there is much desire for enhanced sensitivity. From that point of view, it cannot be denied that the surface-roughened intermediate transfer medium such as in the foregoing 3) is disadvantageous.
Furthermore, as an approach for the writing speed from the system, a system in which plural lasers are arrayed to accelerate writing is broadly practiced. However, solid images recorded by such a system are subject to influence of the laser light intensity distribution and the head period, often deteriorating the uniformity of solid image quality. The method 3) was disadvantageous for such a phenomenon. Thus, this produced problems that the travel to transfer the ink layer was relatively long, so that non-uniformity of laser array units easily occurred due to the delicate difference caused by interrupted supply of the ink or heating conditions, for example.
In view of the foregoing, the present invention was achieved. Thus, it is an object of the invention to provide an transferable image receiving sheet for use in laser thermal transfer, which exhibits superior glossiness even when transferred onto art paper, favorable transferability even onto the final recording medium having an uneven surface, enhanced sensitivity, improved solid image quality and fine-line reproduction; and an imaging method by the use thereof.
It is another object of the invention to disclose a noble imaging method in which the control adhesion balance between layers and cohesive forces of respective layers causes cohesive failure (or cohesion breakdown) of the image receiving layer or interlayer, thereby providing an imaging method exhibiting superior glossiness even when transferred onto art paper, favorable transferability even onto the final recording medium having an uneven surface, enhanced sensitivity, improved solid image quality and fine-line reproduction.
The foregoing object of the invention can be accomplished by the following constitution:
1. A transferable image receiving sheet comprising a support having thereon a heat-softening layer, an interlayer and an image receiving layer in this order from the support, wherein the interlayer has a surface roughness (Ra) of 0.05 to 5 xcexcm and the image receiving layer has a surface roughness (Ra) of 0.01 to 0.4 xcexcm, and the surface roughness (Ra) of the interlayer being greater than that of the image receiving layer.
2. An imaging process by use of an image receiving sheet comprising a support having thereon a heat-softening layer, an interlayer and an image receiving layer, the process comprising the steps of:
(a) imagewise exposing an ink sheet to form an image,
(b) transferring the image from the ink sheet onto an image receiving sheet, and
(c) retransferring the image, together with the image receiving layer, onto a final recording medium,
wherein the interlayer has a surface roughness (Ra) of 0.05 to 5.0 xcexcm and the image receiving layer has a surface roughness (Ra) of 0.01 to 0.4 xcexcm, and the surface roughness (Ra) of the interlayer being greater than that of the image receiving layer.
3. An imaging process using an image receiving sheet comprising a support having thereon a heat-softening layer and an image receiving layer, the process comprising:
forming an image on the image receiving sheet from an ink sheet, and
transferring the formed image and an image receiving layer to a final recording medium,
wherein the following requirement is satisfied:
F1, F2, F3, F4, F5, F7 greater than F6 
wherein F1 is an adhesive strength between the image receiving layer and a lower layer, F2 is an adhesive strength between the image receiving layer and the image, F3 is a adhesive strength between the image receiving layer and the final recording medium, F4 is an adhesive strength between the image and the final recording medium, F5 is a cohesive force of the lower layer, F6 is a cohesive force of the image receiving layer and F7 is a cohesive force of the image;
4. An imaging process using an image receiving sheet comprising a support having thereon a heat-softening layer, an interlayer and an image receiving layer, the process comprising:
forming an image on the image receiving sheet from an ink sheet, and
transferring the formed image and an image receiving layer to a final recording medium,
wherein the following requirement is satisfied:
F11, F12, F13, F14, F15, F16, F18, F19 greater than F17 
wherein F11 is an adhesive strength between the image receiving layer and a lower layer, F12 is an adhesive strength between the image receiving layer and the image, F13 is an adhesive strength between the image receiving layer and the final recording medium, F13 is an adhesive strength between the image and the final recording medium, F15 is an adhesive strength between the interlayer and the heat-softening layer, F16 is a cohesive strength of the heat-softening layer, F17 is a cohesive strength of the interlayer, F18 is a cohesive strength of the image receiving layer and F19 is a cohesive strength of the image.